1. Field of the Invention
The present invention relates to a context generation circuit and method in an apparatus for processing a pixel signal of an image using a joint bi-level image experts group (JBIG) standard, and more particularly, to a circuit for efficiently generating a context with respect to a smaller screen than the horizontal size of a context in a JBIG codec, and a method therefor.
2. Description of the Related Art
Coding for compression and extension of an image signal may be lossy coding or lossless coding. The lossless coding is used by a laser beam printer (LBP) or a fax application product to increase the quality of output. A joint bi-level image experts group (JBIG) has been established as a binary image compression/extension standard.
In a pixel signal processing apparatus using the JBIG standard, a current pixel is encoded by adaptively applying a probability according to the values of peripheral pixels, and the encoding can be performed with respect to up to a predetermined number of pixels (several thousand) adopting two-line and three-line templates.
A conventional method and apparatus for processing a pixel signal of an image is disclosed in U.S. Pat. No. 4,982,292. This apparatus includes two image buffers for storing delayed pixel information necessary for generating a context, a window processing unit required according to the shape of a peripheral pixel, a control unit for selecting a window according to the position of a current pixel, and a memory for temporarily storing compressed output information.
That is, information read by an image scanner is stored in the image buffers, and the position of each pixel is determined with respect to the stored pixel information. A window to be applied according to the determined position is selected. A context is generated by peripheral pixels, using the selected window. Used state information is read from a state table by the generated context. The read state information is applied to an arithmetic encoder, thereby accomplishing coding. This operation is performed in multiple layers, and is also similarly applied to application systems of a single layer.
The application field of the aforementioned apparatus refers to a predetermined number of output pixels (several thousand) or more, as in a facsimile, so an extremely small image is not specially considered. Therefore, the conventional apparatus is effective for a screen that is larger than the horizontal size of a context. When high-speed operation is required, the write and read-out speed of image buffers does not satisfy the actual required operation speed, which impedes the high-speed operation.